While the liquid crystal display cell has been used widely in a variety of electronic equipment such as personal computers and portable electronic devices, there has been much need for improving its performance by increasing its display contrast of images. Japanese Kokai Publication Sho-57-189117 discloses such a technology which comprises disposing two transparent electrode-carrying substrates with the respective electrodes facing each other and a liquid crystal hermetically sandwiched between said substrates, with particles of a colored spacer being dispersed on the entire surfaces of the substrates which are adjoining to the liquid crystal so as to prevent deterioration of the display contrast of images.
The liquid crystal display cell spacer for such a high-contrast liquid crystal display cell must have been colored to a deep shade. While many production methods have heretofore been proposed for the fabrication of such a liquid crystal display cell spacer, they can be roughly divided into the technology which comprises dyeing polymer particles previously manufactured and the technology which comprises dyeing polymer particles in the course of their manufacture.
The technology which comprises dyeing polymer particles previously manufactured includes the following processes.
Japanese Kokai Publication Hei 1-144429 describes a process which comprises treating polymer particles with an acid and then dyeing them. Japanese Kokai Publication Hei-1-207719 discloses a process which comprises subjecting polymer particles to heat treatment at 200 to 700.degree. C. to provide flame-resistant sintered particles. Japanese Kokai Publication Hei-5-165033 discloses a process which comprises coating polymer particles with a conjugated polymer such as polyacetylene. Japanese Kokai Publication Hei-1-200227 describes a process which comprises disposing a metallic layer on the surface of crosslinked polymer particles and oxidizing the metal to the metal oxide.
Japanese Kokai Publication Hei-4-15623 discloses a process which comprises striking ultrafine black metal oxide particles into the surface layers of organic polymer particles, while Japanese Kokai Publication Hei-3-101713 discloses a process which comprises dispersing particles of a polymer containing anionic functional groups in a solution containing an oxidizing agent to let the oxidizing agent adsorbed or impregnated, adding at least one member selected from the group consisting of 5-membered heterocyclic compounds and aromatic hydrocarbons, and causing the mixture to undergo chemical oxidative polymerization. Disclosed in Japanese Kokoku Publication Hei-4-27242 is a process in which particles of a water-soluble polymer available upon polymerization of an ethylenically unsaturated sulfonic acid compound or a salt thereof are dyed with a basic dye.
Furthermore, Japanese Kokai Publication Hei-3-351639 discloses a process which comprises dyeing polymer particles comprising amino resin with an acidic dye in the presence of a solvent at high temperature, while Japanese Kokai Publication Hei-4-363331 discloses a process which comprises dispersing an oily solution of an oily dye uniformly in an aqueous medium, mixing the resulting dye emulsion with an emulsion of polymer particles so as to dye the particles.
However, this technology of coloring polymer particles prepared beforehand not only entails high production costs but also has the drawback that the performance and quality charcteristics of the final product cannot be easily controlled.
The technology which comprises dyeing polymer particles in the course of their manufacture includes the following and other processes. Japanese Kokoku Publication Sho-50-33821, Japanese Kokoku Publication Sho-56-50883, and Japanese Kokoku Publication Hei-4-89805 disclose technologies for producing liquid crystal display cell spacers in which a polymerizable monomer is suspension-polymerized in the presence of a pigment. However, these methods have limitations in the kind of polymerizable monomer that can be used and in production scale and, moreover, the incorporated pigment tends to be exposed on the spacer surface with the result that the pigment itself dissolves out upon exposure to an organic solvent or the like or that impurities in the pigment are liable to dissolve out.
Japanese Kokoku Publication Hei-4-59321 discloses a process for producing a liquid crystal display cell spacer which comprises mixing a lipophilicity-imparted pigment with a monomeric component comprising a polyfunctional vinyl compound and an lipophilic vinyl compound and subjecting the mixture to suspension-polymerization in an aqueous medium. This process is conducive to improvements in the dispersibility of the pigment and solvent resistance but in order to insure a substantial absence of the pigment on the spacer surface, the vinyl compound must be subjected to a suspension polymerization or emulsion polymerization as a post-treatment. Since this process involves two stages of polymerization, the production cost is high of necessity.
Japanese Kokai Publication Hei-7-2913 describes a process for producing a liquid crystal display cell spacer which comprises mixing a pigment uniformly with a (meth) acrylonitrile-containing polyfunctional ethylenically unsaturated component and subjecting the mixture to suspension polymerization in an aqueous medium. However, this technology cannot provide a liquid crystal display cell spacer colored to a deep shade, for although it is conducive to improvements in the dispersibility of the pigment and the mechanical strength and solvent resistance of the spacer, the impurities in the pigment tend to dissolve and diffuse into the spacer to reduce its electrical resistance of the spacer, so that there is a limit to the proportion of the pigment that can be added.
Thus, by the technology of coloring polymer particles in the course of manufacture thereof, too, it is difficult to obtain a liquid crystal display cell spacer with good coloring effect and light shielding effect and physical properties necessary for a spacer in an expedient and efficient manner.